Fire door materials mystery

[wharts02]

Hi,

I have an old fire door which has been removed and cut up but we are at a lost to what the black metal sheet like material is. The door is made up of wood and some Gyproc wallboards and an extra material. I plan to bag it up and take it to an asbestos tip if i cant identity the material. One person has said they doubt its asbestos as the plasterboard would be acting as the fire resistant material. I know it shouldn't have been broken up

Thanks in advance

 

[conny]

It could be some form of intumescent material to slow down/prevent fire spread.
Maybe putting it in the woodwork or doors and windows section may attract more replies.

 

[wharts02]

Thanks conny